I'm not sure what you can plant in there right now, but if you wait until Fall, you will have a lot more options. Fall is a great time to plant stuff, such as perennials, shrubs, and trees. The idea is to plant them after the heat/water stress of the summer.

If you plant anything now, it should probably be just Summer/Annual bedding plants, and you will have to water them very well. These are the typical things like marigolds and geraniums, but others too. (I happen not to be a fan of this sort of planting, but the time of year limits the options.) After they are done blooming, they will die, and you will need to pull them out, then you can plant more permanent stuff in the Fall, and they will look great in the spring.

There are also Fall bedding plants, for Fall color. A popular one in my area is ornamental cabbages. Doesn't sound great, but in late Fall and even Winter, they are very colorful in an otherwise barren garden.
Ornamental Cabbages

Also, in the Fall you can plant bulbs like tulips and daffodils for the following spring.

If you want to plant perennials in the Fall, let me know, and I will tell you some of my faves.

Good luck!